The CSS Working Group has published an updated Working Draft of the CSS Containment Module Level 2. This CSS module describes the contain property, which indicates that the element’s subtree is independent of the rest of the page, as well as content-visibility property, which controls whether or not an element renders its contents at all. This enables heavy optimizations by user agents when used well.
This update publishes about two years worth or refinements, bug fixes, and clarifications, getting closer to stability. A number of open issues remain to be addressed, but the fundamentals are in place. Changes since the last Working Draft are listed in the Changes section.
Please send feedback by either filing an issue in GitHub (preferable) or sending mail to the (archived) public mailing list www-style@w3.org with the spec code ([css-contain-2]) and your comment topic in the subject line. (Alternatively, you can email one of the editors and ask them to forward your comment.)